Spiral-wound membranes and modules containing spiral-wound membranes have been employed in the past in connection with both reverse-osmosis and ultrafiltration operation processes. Typical spiral-wound membranes are described, for example, in U.S. Pat. Nos. 3,367,504 and 3,367,505. Spiral-wound membranes have particular advantages for many applications, due to the high surface-to-volume ratio, low hold-up volume and generally uniform flow patterns, and typically such spiral-wound membranes are less expensive than tubular or hollow-fiber membranes.
Spiral-wound membranes employed in ultrafiltration processes may be used for concentrating cheese whey through the retention of over 95% of the proteins in the cheese whey, as well as the concentration of proteins in milk, or for concentrating enzymes and biologicals produced by fermentation and biological extraction processes. Such spiral-wound membranes also may be employed in the depyrogenating of pharmaceutical process water, concentrating and purifying vaccines and blood fractions, concentrating gelatins, albumin with egg solids, fractionating and concentrating soy whey protein, recovering textile sizing from desized waste, recovering lignosulfonate from waste streams, recovering spent tannery baths and waste solvents and otherwise upgrading or separating liquids.
Typically, a spiral-wound membrane or envelope is wound up about a perforated central tube and is disposed within a module housing. One impediment to the application of spiral membrane modules, particularly in the sanitary field, such as in the dairy and pharmaceutical field, has been the effective cleaning and sanitizing around the exterior of the module in the annular space between the membrane module and the module housing. Spiral membrane modules must be cleaned and sanitized easily in a variety of sizes in the field and during operation, particularly when used with the concentration of whey in the dairy field.
Attempts to provide for the cleaning and sanitizing of the annular space about the exterior of the spiral-wound membrane have included the use of a so-called "leaky brine seal", as set forth in U.S. Pat. No. 4,064,052, issued Dec. 20, 1977. This patent discloses a spiral-wound module within a housing module, wherein one or more small holes are placed in an annular lip seal within the annular space between the spiral-wound membrane and the interior wall of the housing. This lip seal, containing a plurality of holes, permits a small controlled flow of the feed stream to by-pass the module continually through the annular space and prevents any stagnation or accumulation of product or residue behind the seal. However, this approach is not wholly satisfactory and has various manufacturing cost and operational difficulties associated with its practice.
Therefore, it is desirable to provide an improved spiral-wound membrane apparatus which provides ease in maintaining the sanitation and cleanliness of the module in operation and in the field.